Abstract: A dismount brake device (1) is tethered by a cable (4) to a snowmobile rider (3). Pulling on the cable (4) displaces a trigger (17) which frees a piston (34). The piston (34) is biased by a main spring (39) to decrease the volume of a chamber (11) containing hydraulic fluid and which is interconnected to the brake line (13). A plunger (36) extends from the head of the piston (34) and seals a port (40) leading to the master cylinder (42). As the volume of the chamber (11) continues to decrease, the pressure in the brake line (13) reaches a value that will activate the brakes and stop rotation of snowmobile track (47). Activation of the brake handle (46) resets the device (1) for further use. An alternate embodiment (48) utilizes a solenoid (50) instead of the tether (4) to physically move a modified trigger (56) when a switch senses that the seat (64) of the snowmobile (2) is unoccupied.